A titanium oxide-based photocatalyst absorbs near-ultraviolet, and exhibits a strong oxidative decomposition ability so as to oxidatively decompose and detoxify environmental contaminants, such as various organic substances and NOx. In a case wherein a base plate is coated with titanium oxide-based photocatalysts, upon exposure to light, the surface of the base plate exhibits a photo-induced ultra hydrophilic property, and becomes easily soluble in water, such that fouling on the surface of the base plate can be easily washed off by water. In other words, a titanium oxide-based photocatalyst has an ability to decompose fouling by the action of light, and an ability to facilitate a removal of fouling by water. Because of these abilities, titanium oxide-based photocatalysts have been put into practical use as self-cleaning materials which constantly keep surfaces clean.
The following methods are known as techniques for forming a film of titanium oxide-based photocatalysts on a base plate:
(i) a technique wherein suspension of micro particles of titanium oxide, including a suitable binder component, is coated, and dried so as to form a film (see Patent Document 1),
(ii) a technique wherein titanium oxide sol, obtained by a sol-gel method, is coated and fired (see Patent Document 2),
(iii) a technique wherein solution of an organic titanium compound is coated so as to form a film, and fired so as to produce a photocatalytic film (see Patent Document 3),
(iv) a technique wherein a titanium compound, such as titanium peroxide, is coated and dried so as to form a film (see Document 4),
(v) a technique wherein thin sheet micro particles of titanium oxide are coated and fired so as to form a photocatalytic film (see Patent Document 5),
(vi) a technique wherein titanium oxide film is formed by a gas-phase method, such as sputtering (see Patent Document 6).    Patent Document 1: Unexamined Japanese Patent Publication No. 11-228113    Patent Document 2: Unexamined Japanese Patent Publication No. 11-256342    Patent Document 3: Unexamined Japanese Patent Publication No. 09-278489    Patent Document 4: Unexamined Japanese Patent Publication No. 07-100378    Patent Document 5: Unexamined Japanese Patent Publication No. 2005-290369    Patent Document 6: Unexamined Japanese Patent Publication No. 2000-290533